1. Field of the Invention
The present invention relates to a turntable structure, and in particular to a turntable structure that controls function selection for a media player.
2. Description of the Related Art
Referring to FIG. 1, a media player 1 uses a conventional turntable structure 10 to control and select the function provided thereby.
Referring to FIG. 2A and FIG. 2B, the conventional turntable structure 10 is composed of a base 12, a bearing assembly 14, a rotating assembly 16 and a rotating shaft 18. The base 12 has a central post 20 formed thereon. The bearing assembly 14 is pressed on the central post 20. The rotating shaft 18 is fit into the central post 20 and connected to the rotating assembly 16. In addition, a plurality of toothed portions (not shown) are disposed on the bottom of the rotating assembly 16, and a sensor (not shown) is disposed on the media player 1. When the rotating assembly 16 rotates, the sensor detects the number of the toothed portions which have rotated to determine the rotary position of the rotating assembly 16 and outputs a corresponding signal to the media player 1.
Nevertheless, the conventional turntable structure 10 has many drawbacks. The bearing assembly 14 is directly pressed on the central post 20 formed on the base 12. When the bearing assembly 14 is pressed on the central post 20, force applied to press the bearing assembly 14 causes breakage between the base 12 and the central post 20.
In addition, because the base 12 and the central post 20 are composed of plastic and the bearing assembly 14 is composed of metal, the thermal expansion coefficient of the central post 20 is different from and greater than that of the bearing assembly 14. Additionally, there must be a tight fit between the central post 20 and the bearing assembly 14. When ambient temperature rises, severe compression occurs between the inner ring 14a of the bearing assembly 14 and the central post 20 due to thermal expansion. Thus, the central post 20 may be deformed or break. In another aspect, when the ambient temperature decreases, the bearing assembly 14 may be separated from the central post 20 because of deformation of the central post 20. Although the bearing assembly 14 may not completely separate from the central post 20, the horizontal positions of the bearing assembly 14 and the rotating assembly 16 change due to the deformation of the central post 20, such that the number of toothed portions which have rotated is inaccurately detected by the sensor.
Hence, there is a need to provide an improved turntable structure to overcome the aforementioned problems. The turntable structure includes a retaining ring. The retaining ring is disposed between the bearing assembly and the central post such that the bearing assembly snugly encircles the central post. Meanwhile, a gap exists between the retaining ring and the central post, such that undesirable effects as mentioned above are prevented when the ambient temperature changes.